In [1]}, the authors propose FNet, another alternative which resembles PoolFormer architecture. In particular, a 2D FFT is applied to the input \({\mathbf {X}}_i\)  before being passed through an MLP
\(f_{FNET}({\mathbf {X}}_i) = \sigma (\mathbf {F}_{s}\mathbf {X}_i\mathbf {F}_d^\top \mathbf {W}_1)\mathbf {W}_2\) 
